The present invention relates to the structure and methods of connecting terminals of a high-density information display unit having perpendicular layered electrodes or matrix electrode constructions.
In matrix display units such as liquid crystal displays, plasma displays or EL displays, the density of information display becomes higher and the quality of displayed information is better as the number of lines or scanning lines is larger. However, the more the scanning lines, the period of time required for applying signals per line, that is, a duty cycle, is reduced and the margin for crosstalk is also reduced. Where liquid crystals are employed as display elements, no sufficient contrast is available in such high-density liquid crystal displays for the reasons that the liquid crystals have no steep transmission-voltage characteristics and suffer from a slow response. Various solutions to such problems have been proposed. One proposed solution is to develop a liquid crystal material having applied voltage vs. light transmission characteristics with a sharp threshold. According to another proposal, a matrix addressing system is optimized to increase the drive margin (.alpha.=Von/Voff). Still another solution is to increase an apparent resolving power through an improvement of the electrode construction. More specifically, as shown in FIG. 1(A) of the accompanying drawings, signal electrodes are divided into upper electrodes Y1, Y2, . . . , Yn and lower electrodes Y1', Y2', . . . , Yn, and the upper and lower signal electrodes are shared in common as opposed to scan electrodes. Alternatively, as shown in FIG. 1(B), adjacent signal electrodes Yj, Yj+1 are entered as comb teeth in a single scanning electrode Xi. According to a still further proposal, as shown in FIG. 2, there is provided one liquid crystal panel having scanning electrodes 2 and a signal electrode 3 disposed between glass plates 1, 4 and another liquid crystal panel composed of scanning electodes 2a and signal electrodes 3a positioned between a glass plate 1' and the glass plate 4, the liquid crystal panels being independently driven with the glass plate 4 being shared by the two liquid crystal panels.
According to the first and second solutions, it is not necessary to modify the construction of the liquid crystal panel, but no drastic increase in the number of drivable lines can be expected. The third proposal renders the liquid crystal panel complex in structure, but nevertheless can increase the number of drivable lines twice, or 2.sup.2 times. Though the third solution can thus increases the drivable lines, it also increase the number of terminals of signal electrodes twice, or 2.sup.2 times.
As illustrated in FIG. 3, an ordinary liquid crystal display panel has glass plates 4, 5, and signal electrodes 3 and scanning electrodes 2 which are formed on inner surfaces of the glass plates 4, 5. The signal electrodes 3 and the scanning electrodes 2 are not positioned on the same plane. A liquid crystal 6 is sealed between the glass plates 4, 5 by sealing resin 7. For incorporating the foregoing packaging processes, it is necessary to transfer the scanning electrodes 2 onto the signal glass plate 4 by a transfer material 8 such as an electrically conductive silver (Ag) paste to form a terminal of the scanning electrodes 2 flush with the signal electrodes 3. However, such electrode transfer has the following problems:
(I) The glass plates require regions for transferring the electrode, and cannot be rendered smaller in size; PA1 (II) An additional step of transferring the electrode is needed, resulting in an increased cost; and PA1 (III) The transfer material 8 tends to peel off at its interface with the glass plates 4, 5 due to different coefficients of thermal expansion of the sealing resin 7 and the transfer material 8, with the consequence that a conduction failure occurs and thus operation reliability is poor.
Where the third proposed solution is employed for connecting the liquid crystal panel to a wiring board without transferring the electrode, a marginal edge of the wiring board on which liquid crystal driver circuit elements are mounted is bent for electrical connection to terminals of the liquid crystal panel through the use of electrically conductive anisotropic rubber. With such a connecting process, as shown in FIG. 5, a glass plate 4 is employed to form a liquid crystal cell housing therein signal electrodes 3 and scanning electrodes 2, and a liquid crystal 6 is interposed between the electrodes 2, 3 and sealed at its periphery by a sealing material 7, thus constituting a liquid crystal panel. The terminals of the electrodes 2, 3 extend over an outer surface of the glass plate 4 and are connected electrically and mechanically to an end of a wiring board 11 with driver circuit elements 12 thereon through a gripper 10, there being a body 9 of electrically conductive anisotropic rubber (elastomer) interposed between the glass plate 4 and the wiring board 11. With this arrangement, the scanning electrodes 2 connected to the wiring board 11 are disposed below an end of the latter, and it is quite tedious and time-consuming to insert a body 13 of electrically conductive anisotropic rubber between the glass plate 4 and the end of the wiring board 11. It has been difficult to transfer an electrode to one of the glass plates with a transfer material in a matrix liquid crystal panel composed of a multiplicity of lines. Since terminal electrodes are mounted on confronting surfaces of the glass plates in such a liquid crystal panel, the liquid crystal panel cannot easily be mechanically secured to the wiring board on the side of the scanning electrode 2 through the above connecting process.